Mutton bird / Wedge-tailed shearwater / Puffinus pacificus / Family - Procellariidae
Large numbers of wedge-tailed shearwaters can be seen on the Great Barrier Reef, particularly in the Capricorn/Bunker group.
Wedge-tailed shearwaters are one of several species, known as 'mutton-birds,' whose chicks are harvested as food by Indigenous people in Australia and New Zealand. Other mutton-bird species include the flesh-footed shearwater (Puffinus carnipes), and the sooty shearwater (Puffinus griseus), which has the distinction of being the world's most numerous seabird.
Shearwaters spend their whole life at sea, except when breeding. Like their close relatives, the albatrosses and petrels, they live almost constantly on the wing.
The distinguishing feature of shearwaters is their tube-nosed bill, which is long and slightly hooked at the tip with two nostrils that appear as a double tube at the base of the upper mandible. Scientists sometimes refer to the whole group as 'The Tube Noses.' Shearwaters obtain essential moisture by drinking seawater. The tube nose enables shearwaters to expel excess salt from their bodies.
Like most members of their family, which includes albatrosses, petrels, fulmars, storm-petrels and prions, shearwaters are clumsy on the ground and often crash when returning to the nest. They also require a 'runway' such as a log or uphill slope to take off.
Shearwaters can be seen feeding at sea during the day, often sitting on the surface and dipping their head under the water to feed.
In late afternoons and evenings during the breeding season, large groups of birds gather close to shore while they wait for darkness to fall. As soon as it is dark, they fly ashore to their burrows. The cacophony of millions of shearwaters wheeling and swooping over their breeding grounds is akin to the noise of a large rugby crowd after a goal has been scored. It is one of the most unforgettable experiences of the natural world.
Some shearwaters nest on open ground or on ledges, however most species nest in burrows or on cavities in rocks. The burrow is dug by the birds themselves. They use plant material to line the nest.
Shearwaters and their relatives are mostly Southern Hemisphere species that breed from Antarctica to the tropics. They nest on islands, rocky shores, cliff-tops and hills, often in colonies of several million pairs, and sometimes a long way from the sea. Hutton's shearwater (Puffinus huttoni), for example, nests above the snow-line at 2000m on the Kaikoura mountains of New Zealand's South Island.
Shearwaters are extremely reliable breeders. They range over hundreds of thousands of kilometres of open ocean, and yet manage to arrive over their breeding grounds on precisely the same night year after year.
A single white egg, large from the size of the bird is laid. Incubation varies from 40 to 60 days, depending on the species, and both parents sit for alternate periods of 2-12 days.
The eggs and young can survive periods of neglect, an adaptation to long gaps between changeover of incubation and infrequent visits of the parents. Young chicks are only guarded for the first 2 to 3 days, and then they are only visited at intervals for feeding. Many species can defend themselves by spitting quantities of oil.
Young chicks are very large and fat, however lose this while the feathers are growing. The whole growth period takes 45-55 days in small species and up to 100-135 days in the largest.
Baby shearwater's are fed with fish and shrimps regurgitated by the adults.
Shearwaters eat crustaceans, organic plankton, squid, fish, and in some cases floating scraps discarded from fishing boats.
Great care should be taken when visiting shearwater breeding islands. The ground may be honey-combed with burrows, and it is easy to break a leg or crush eggs by sinking through the ground into a burrow by mistake. Some birds are easily frightened and may desert their nest with eggs and chicks.
Apart from human disturbance, natural pressures such as storms and cyclones also affect seabird populations. These natural disasters can be massive; however can be tolerated because they are not regular. The effects of human activity, repeated disturbances, is more likely to be a far worse contributor to the recovery of populations from natural disasters or even prevent the recovery altogether.
There are many ways we can protect seabirds, shorebirds and their habitats. For example:
- During the breeding season, some islands of the Great Barrier Reef are closed to all visitations. During summer, the Brook Islands are completely off limits protecting the thousands of Pied Imperial Pigeons, which nest there.
- Special fire regimes are introduced to carefully manage vegetated islands and cays.
- Preservation of the mangrove forests is vital, not only for birds and other animals, but also to maintain the natural tidal flows and possible destructive effects of cyclones.
- Pollution by excessive sediment, rubbish and waste affects the important mangroves, mudflats and inner reef, altering the food supplies.
- Controlling feral animals will help to reduce predation on nesting birds and young.
- Control of introduced plants will allow native vegetation to regrow.
- Dunes are a natural part of beaches. Controlling beach access and vehicles will help to maintain these features and protect vulnerable ground-nesting birds.